In many cities, the disposal of residential garbage is carried out as follows. Each household puts its garbage into a polyethylene garbage bag designated by the city and places the filled bag in a designated spot outside the house on an appointed day for collection. The garbage bags are then collected by city garbage trucks.
A problem associated with this conventional disposal method is that garbage bags left outside are often ripped open by foraging animals like cats, dogs, rats, squirrels, and raccoons before garbage trucks can collect them, thereby scattering the garbage.
There are similar known problems with wiring insulation. For example, in building construction, cable such as electrical cable comprising an insulator sheath made from synthetic resin typically is laid in ceilings or under floors where it is susceptible to being bitten by rats and squirrels infesting the building. As a result of the insulation being stripped off the wiring, electricity leakage, short-circuits, and fires may take place. For another example, backpackers leaving their vehicles unattended in parking lots for several days may return to find that the insulation has been chewed from the vehicle wiring harness by wild rodents.
A number of animal repellents are known, but none of them is satisfactory both in terms of effect and cost. In the prior art, repellents typically are impregnated into a powdery support, spread or sprayed directly on an article, or manufactured as a component of shaped articles having a repellent effect.
U.S. Pat. No. 5,571,582, the relevant disclosure of which is incorporated herein by reference, discloses a garbage bag or container formed of a synthetic resin composition containing 10 to 7000 ppm by weight of at least one compound selected from a group consisting of ester of salicylic acid such as methyl salicylate, ethyl salicylate, propyl salicylate, n-butyl salicylate, iso-butyl salicylate and iso-amyl salicylate, menthol and camphor. Polyolefins such as polyethylene, polypropylene, ethylene/vinyl acetate copolymer, ethylene/acrylic acid ester copolymer, and poly(1-butene) are preferable. The synthetic resin composition can be shaped into various shaped articles such as bags, bottles etc. by various methods for example extrusion, injection and blow molding. Animals such as cats, dogs, rats, and crows dislike the particular odors of ester of salicylic acid, menthol, and camphor. A repellent effect is given to shaped articles by incorporating these odorants into the synthetic resin before shaping. It was found that the repellent effect was observed if shaped articles contained more than 1 ppm by weight of these odorants, but it may be necessary that more than 10 ppm by weight of these odorants be contained in the composition for shaping in consideration of the loss during shaping. The disclosure teaches that the concentration of these odorants should be high, but if the concentration is higher than 7000 ppm bleeding may occur, so to obtain the best result, the concentration is preferably 10 to 5000 ppm by weight in the composition. If an elastomer is added to the synthetic resin composition, slow and prolonged shedding of the odorants is expected, meaning that the shaped articles comprising the composition can repel animals for a longer time.
In forming a synthetic resin composition using the odorant methyl salicylate, 20 parts by weight of methyl salicylate was added dropwise to 80 parts by weight of pellets of ethylene/vinyl acetate copolymer (EVA) (“Mitsubishi Polyethyl EVA V601S”, trade name, sold by Dia Polymer Co., Ltd.) and left for 24 hours at room temperature so that methyl salicylate was impregnated into the EVA pellets. This type of blend is referred to herein as a “master blend”. In the same manner, three samples of EVA pellets containing 20% by weight of ethyl salicylate, iso-butyl salicylate, and liquid menthol, respectively, were prepared. Then 2.5 parts by weight of these master blends were mixed respectively with 97.5 parts by weight of polypropylene pellets (PP) (“Mitsubishi Polypro”, trade name, sold by Dia Polymer Co., Ltd.). The resulting mixed pellets were extruded and pelletized in readiness for forming into sheet form for manufacturing a garbage bag or container.
The ratio of EVA to odorant in a master blend as taught in the prior art is thus 4:1, and the odorant is impregnated into the EVA by the method of allowing the two components to stand in contact together for 24 hours.
A shortcoming of this method is that the odorant does not become well distributed through the EVA, and a relatively large percentage of EVA (which is a relatively expensive polymer), i.e., 2.5% master blend, is required to achieve the desired odorant concentration in the garbage bag or container.
Another shortcoming of this method is that the created master blend does not produce uniform absorption of odorant into the EVA, resulting in inconsistent scent strength throughout the finished product.
US Patent Application Publication US 2006/0110421, the relevant disclosure of which is incorporated herein by reference, discloses a similar composition and process for forming an article or container but extends the range of odorant composition to 10-15,000 ppm before bleeding occurs.
This reference discloses that the odorant may be incorporated into the synthetic resin composition by dropwise addition of a predetermined amount of the odorant onto pellets of the synthetic resin to be used. Thereafter, the pellets may be left alone without mixing for a predetermined amount of time at a predetermined temperature such that the odorant is impregnated into the pellets. The thus treated pellets (a master blend) may be mixed with untreated pellets to adjust the concentration of the odorant to the desired level. Preferably, the pellets treated with the odorant are left alone without mixing for a period of time ranging from several hours to 24 hours in order to have the odorant impregnated therein. Preferably, the pellets treated with the odorant are left alone at room temperature. The shortcomings of this method are noted above with respect to U.S. Pat. No. 5,571,582.
As an alternative to the dropwise addition of a predetermined amount of the odorant onto pellets of the synthetic resin, pellets of the synthetic resin may be soaked in the liquid form of the odorant. This method is wasteful because it leaves an excess of liquid odorant on the pellets that does not enhance the final activity of the synthetic resin composition in the article.
As an alternative to both dropwise addition and soaking in liquid odorant, a predetermined amount of odorant may be dissolved in a solvent, such as diethyl ether, and sprayed onto pellets of the thermoplastic polymer. The solvent may be thereafter eliminated by, e.g., air-drying at room temperature. This method is inferior because an additional compound, the solvent, is required and must be accommodated as a waste product of the process, thus increasing the manufacturing cost.
What is needed in the art is a synthetic resin composition having improved penetration of odorant into the resin that therefore can be manufactured with an overall lower level of odorant and impregnated resin, at lower cost.
What is further needed in the art is an improved method for impregnating odorant into a resin that requires less odorant, leads to more uniform distribution of odorant in the resin, and requires a lower level of master blend in the final synthetic resin composition to achieve the same or better final activity of the odorant in the article.
It is a principal object of the invention to reduce the cost of manufacture of a synthetic resin composition.
It is a further object of the invention to improve and simplify the manufacturing process for a synthetic resin composition including an animal-repelling odorant.